3 files changed, 31 insertions, 15 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index c61934fbf22a..64a619d47d34 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -47,8 +47,9 @@ extern bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn);
 extern unsigned long set_phys_range_identity(unsigned long pfn_s,
                                              unsigned long pfn_e);
 
-extern int m2p_add_override(unsigned long mfn, struct page *page);
-extern int m2p_remove_override(struct page *page);
+extern int m2p_add_override(unsigned long mfn, struct page *page,
+                            bool clear_pte);
+extern int m2p_remove_override(struct page *page, bool clear_pte);
 extern struct page *m2p_find_override(unsigned long mfn);
 extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
 
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 141eb0de8b06..2d2b32af3a1d 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -650,7 +650,7 @@ static unsigned long mfn_hash(unsigned long mfn)
 }
 
 /* Add an MFN override for a particular page */
-int m2p_add_override(unsigned long mfn, struct page *page)
+int m2p_add_override(unsigned long mfn, struct page *page, bool clear_pte)
 {
         unsigned long flags;
         unsigned long pfn;
@@ -662,7 +662,6 @@ int m2p_add_override(unsigned long mfn, struct page *page)
         if (!PageHighMem(page)) {
                 address = (unsigned long)__va(pfn << PAGE_SHIFT);
                 ptep = lookup_address(address, &level);
-
                 if (WARN(ptep == NULL || level != PG_LEVEL_4K,
                                         "m2p_add_override: pfn %lx not mapped", pfn))
                         return -EINVAL;
@@ -674,10 +673,9 @@ int m2p_add_override(unsigned long mfn, struct page *page)
         if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
                 return -ENOMEM;
 
-        if (!PageHighMem(page))
+        if (clear_pte && !PageHighMem(page))
                 /* Just zap old mapping for now */
                 pte_clear(&init_mm, address, ptep);
-
         spin_lock_irqsave(&m2p_override_lock, flags);
         list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
         spin_unlock_irqrestore(&m2p_override_lock, flags);
@@ -685,7 +683,7 @@ int m2p_add_override(unsigned long mfn, struct page *page)
         return 0;
 }
 
-int m2p_remove_override(struct page *page)
+int m2p_remove_override(struct page *page, bool clear_pte)
 {
         unsigned long flags;
         unsigned long mfn;
@@ -713,7 +711,7 @@ int m2p_remove_override(struct page *page)
         spin_unlock_irqrestore(&m2p_override_lock, flags);
         set_phys_to_machine(pfn, page->index);
 
-        if (!PageHighMem(page))
+        if (clear_pte && !PageHighMem(page))
                 set_pte_at(&init_mm, address, ptep,
                                 pfn_pte(pfn, PAGE_KERNEL));
                 /* No tlb flush necessary because the caller already
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 3745a318defc..fd725cde6ad1 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -466,13 +466,30 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
                 if (map_ops[i].status)
                         continue;
 
-                /* m2p override only supported for GNTMAP_contains_pte mappings */
-                if (!(map_ops[i].flags & GNTMAP_contains_pte))
-                        continue;
-                pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
+                if (map_ops[i].flags & GNTMAP_contains_pte) {
+                        pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
                                 (map_ops[i].host_addr & ~PAGE_MASK));
-                mfn = pte_mfn(*pte);
-                ret = m2p_add_override(mfn, pages[i]);
+                        mfn = pte_mfn(*pte);
+                } else {
+                        /* If you really wanted to do this:
+                         * mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
+                         *
+                         * The reason we do not implement it is b/c on the
+                         * unmap path (gnttab_unmap_refs) we have no means of
+                         * checking whether the page is !GNTMAP_contains_pte.
+                         *
+                         * That is without some extra data-structure to carry
+                         * the struct page, bool clear_pte, and list_head next
+                         * tuples and deal with allocation/delallocation, etc.
+                         *
+                         * The users of this API set the GNTMAP_contains_pte
+                         * flag so lets just return not supported until it
+                         * becomes neccessary to implement.
+                         */
+                        return -EOPNOTSUPP;
+                }
+                ret = m2p_add_override(mfn, pages[i],
+                                       map_ops[i].flags & GNTMAP_contains_pte);
                 if (ret)
                         return ret;
         }
@@ -494,7 +511,7 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
                 return ret;
 
         for (i = 0; i < count; i++) {
-                ret = m2p_remove_override(pages[i]);
+                ret = m2p_remove_override(pages[i], true /* clear the PTE */);
                 if (ret)
                         return ret;
         }